Field of the Invention
The present invention relates to an ablation method of applying a laser beam to a die attach film (DAF) to perform ablation.
Description of the Related Art
A plurality of devices such as ICs, LSIs, and LEDs are formed on the front side of a wafer such as a silicon wafer and a sapphire wafer so as to be partitioned by a plurality of division lines. The wafer is divided into the individual devices by any dividing apparatus such as a cutting apparatus and a laser processing apparatus. These devices are widely used in various electrical equipment such as mobile phones and personal computers. As a method of dividing the wafer into the individual devices, a dicing method using a cutting apparatus called a dicing saw is widely adopted. In this dicing method, a cutting blade having a thickness of about 30 μm is rotated at a high speed of about 30000 rpm and fed in the wafer to cut the wafer, thus dividing the wafer into the individual devices. The cutting blade is formed by bonding abrasive grains of diamond, for example, with metal or resin.
In recent years, it has been desired to further reduce the weight and size of electrical equipment such as mobile phones and personal computers, so that thinner devices have been required. As a technique of dividing a wafer into thinner devices, a so-called dicing before grinding process has been developed and put to practical use (see Japanese Patent Laid-open No. 2002-118081, for example). This dicing before grinding process includes the steps of forming a division groove having a predetermined depth (corresponding to the finished thickness of each device) along each street (division line) on the front side of a semiconductor wafer and next grinding the back side of the semiconductor wafer to expose each division groove to the back side of the semiconductor wafer, thereby dividing the semiconductor wafer into the individual devices. By this dicing before grinding process, the thickness of each device can be reduced to 100 μm or less.
Frequently adopted as a method of mounting to a lead frame the devices divided from each other by the dicing before grinding process is a method including the steps of attaching an adhesive film for die bonding called a die attach film (DAF) to the back side of each device and mounting each device through the DAF to the lead frame. In this mounting method, the following technique has been studied. A protective tape is previously attached to the front side of the wafer divided into the individual devices by the dicing before grinding process, so that the devices are united by the protective tape. Accordingly, the DAF is attached to the back side of the wafer divided into the individual devices, and the DAF is next attached to an adhesive tape supported to an annular frame. Thereafter, the protective tape is peeled off from the front side of the wafer.
Thereafter, the wafer with the DAF supported to the annular frame is held under suction on a chuck table of a laser processing apparatus, and a laser beam is applied to the DAF through division grooves formed in the wafer, thereby dividing the DAF into parts respectively corresponding to the individual devices.